This invention relates in general to a clothes washing machine or a combined clothes washing and drying machine of the household type, and more particularly to a washing machine, or a combined washing and drying machine, having a molded plastic washing tub with improved means to retain and hold an associated ballast member or counterweight in place.
Molded plastic washing tubs for clothes washing machines are known in the art to comprise a generally rigid structure forming the cylindrical peripheral wrapping or outer wall, an associated circular rear or bottom wall, and a circularly shaped front or top wall. The front or top wall is sometimes separable and is capable of being joined to the remaining tub components with known fastening means.
Appropriate heavy elements, acting as counterweights or ballasts, are usually associated with, ie. fixed to, the tubs, in order to counterbalance the tub, ie. to increase its inertia, and as a consequence limit oscillations that are generated on the tub during spin-extraction phases. When the rotating or spin drum holding the washload is driven to rotate at its highest revolution speed, ie. a speed that is considerably higher than the one at which the same spin drum typically rotates during washing and rinsing phases, the counterweights or ballast limit undesirable oscillatory movement of the tub.
Such oscillations are induced by conditions arising from an uneven distribution of the washload along the cylindrical outer wall of the rotating drum. If no measure is taken to dampen such oscillations, a number of drawbacks and problems well known in the art arise.
Counterpoising or ballast means for clothes washing machine tubs of the subject type are known to be formed by one or more blocks of concrete or various similar masses of material with a high specific weight. The counterpoising blocks or masses are first separately formed in advance to an appropriate shape and are then attached in a suitable arrangement to the washing tub of the respective washing machine by means of any of a number of removable fastening means such as screws, bolts, nuts, and the like.
However, these types of counterweights have a drawback in that they require a relatively long time for the concrete to be prepared and duly hardened. The concrete blocks furthermore carry with them the risk of coming or breaking off seats provided for their attachment to the tub due to vibrations that are generated by the operation of the machine. The vibrations can sometimes actually cause the concrete blocks to collapse and disintegrate.
Additional types of counterweights for clothes washing machine tubs are known, for example Italian Utility Model No. 34081/B/89, discloses concrete blocks that are prepared in advance. A plastic material is then applied onto the block by an overinjection molding technique so as to form an appropriately shaped enclosed wrapping capable of both preventing the blocks from becoming unduly displaced and undesirably breaking off. The blocks are attached in a traditional manner to the tub of the washing machine.
Even with the plastic wrapped blocks, however, there is the drawback of the relatively long time required for the concrete blocks to be prepared and hardened. This is a clear disadvantage from an economic point of view. Furthermore, the blocks require a rather complicated manufacturing process due to the overinjection of the plastic wrapping.
Among the various solutions suggested or proposed in this connection, a particularly interesting one is disclosed in the Italian Patent Application No. PN92A000002 titled "Improvement in the ballast arrangement for clothes washing machines".
The Italian patent application discloses a container which is associated or fixed to a plastic washing tub and is capable of being filled with appropriate ballasting means, preferable water, when the machine is installed. The advantage of such a solution resides in the fact that clothes washing machines produced according to this concept are much lighter in weight and, therefore, more convenient to handle during transportation and installation. The clothes washing machines are also less expensive due to both the reduction in transportation costs and the savings achieved through avoidance of manufacturing costs of a traditional ballast made of a heavy-weight material such as cast-iron or concrete.
Even this solution, however, has a drawback in that it fails to identify in a sufficiently clear and complete way the most adequate technique to be used to manufacture the washing tub of plastic material with the ballast containing arrangement associated therewith. This of course makes practical implementation of the solution rather problematic.
It is therefore a purpose of the present invention to overcome these drawbacks by providing a plastic tub for clothes washing machines and an associated counterweight, made of high specific-weight material and enclosed in a protective shell of plastic material that is capable of being attached to the plastic tub in such a way to make it possible to easily and quickly install the shell to the structure of the tub.